The present invention generally relates to a practical system of measuring road surface friction using an auxiliary wheel and more particularly to a system wherein a switch in the cab deploys the measuring wheel and the in-cab display gives a continuous reading of road surface friction as soon as the wheel rotates. The road friction tester (“RFT”) is designed for use in the trucking industry to determine road surface grip where driving conditions may be hazardous.
Most currently used, practical, devices, which measure road friction, require either a dedicated vehicle for operation or are towed behind a vehicle. It is desirable to measure the road traction, for example, in the winter as ice is forming and while snow and ice is being removed from the road. The knowledge of road condition while the road is being treated is helpful in determining appropriate treatment of the road surface. Cost savings can be realized, but road safety would also be increased which would help all motorists. DE 34 09 040.1 recognizes the need to measure the lateral force exerted against a wheel rotating in a straight line. No practical implementation for this recognition is given, however.
Most road friction measurement devices require a wheel to be skidded against the road in the same direction as the vehicle. The force, which resists forward motion, is measured. This particular layout requires a tire, which runs at a slower of faster speed than road speed. This requirement results in high tire wear, water must flood the contact patch and very large forces are developed. There have been other means of measuring the friction using a tire or wheel skew to the motion vector of the vehicle, but many have been abandoned due to complexity or reliability issues.
U.S. Pat. No. 5,821,434 is a method for determining the grip performance of a vehicle. To measure the grip performance of a vehicle, a practical method of measuring the lateral force developed by a tire was required. The details of this method are described in U.S. Pat. No. 5,821,434. In synopsis, the rotating member and its bearing support are isolated from the wheel hangar by a linear bearing. The linear bearing allows the freedom of motion necessary for measurement of the force developed between the wheel support bearing and the hangar and an appropriately designed load cell measures this force. This patent is a development of this previous patent in that a similar method of determining the force is used, but the focus of the patent is to determine the frictional capacity of the road as opposed to the grip performance of a vehicle. The GEM device is the commercial embodiment for measuring grip performance of a vehicle.
The present invention is unique in that it extends the GEM device concept for taking road condition measurements for determining the condition of the road under adverse weather conditions in real time.